1. Field of the Invention
The present invention relates to a switching regulator, and particularly to a switching regulator with improved low power consumption.
2. Description of the Related Art
In recent years, information terminals such as cellular phones, PDAs (Personal Digital Assistants), etc., have employed devices that require higher voltage than the battery output voltage and/or devices that require lower voltage than the battery output voltage. In such cases, i.e., in a case in which the required voltage is higher than or lower than the battery voltage, a switching regulator is employed that steps up or steps down the battery voltage and thereby creates a suitable voltage to be supplied to each device.
The pulse width modulation method is widely employed as a method employed in a control circuit for controlling ON/OFF switching of a switching device element of a switching regulator. In the pulse width modulation method, a comparison is made between the output voltage of the switching regulator and a reference voltage which is a target value, and the pulse width of the driving signal is adjusted such that the error voltage thereof exhibits the minimum value. With the pulse width modulation method, the ON time ratio during which the switching device element is ON, i.e., the duty ratio, is adjusted so as to control the step-up ratio according to the battery voltage, thereby maintaining the output voltage at a constant voltage.
There is a great demand for such a switching regulator having improved conversion efficiency in the light-load state in which a low load current is applied. A technique in which the switching operation is stopped in the light-load state, thereby reducing the power consumption (electric current consumption), is disclosed in the Patent document.
[Patent Document 1]
Japanese Patent Application Laid Open No. 2000-50626